1. Field of the Invention
The invention relates to a planting device, and more particularly, to a planting device for planting a plurality of solder balls on a chip.
2. Description of the Prior Art
In recent years, along with the fast development of electronic technology accompanied with the appearances of LSI, VLSI, and ULSI, the density of a silicon chip has risen continuously. Due to the I/O foot-number drastically increasing, the power that each silicon chip consumes has also increased. Therefore, the conventional dual in-line package (DIP) and the quad flat package (QFP) cannot always satisfy physical requirements anymore. The presence of the ball grid array package (BGA Package) then filled up this gap.
Please refer to FIG. 1. FIG. 1 is a cross-sectional diagram of a ball grid array package 10 of the prior art. The ball grid array package 10 comprises a substrate 12. The substrate 12 comprises a Cu trace layer 6 installed under the substrate 12, a plurality of solder ball pads 14 installed on the surface of the Cu trace layer 16, and a solder mask 18 covered on the surface of the Cu trace layer 16 beyond the solder ball pad 14. The solder ball pad 14 is installed on the surface of the Cu trace layer 16, making use of the solder mask 18 as the isolation layer. After the ball grid array package 10 is achieved, a plurality of solder balls 20 are used to fix the package 10 on a printed circuit board (PCB) 22 so that the ball grid array package 10 and the printed circuit board 22 can be electrically connected to each other. The ingredients of the solder ball is an alloy of 63% tin and 37% lead.
The main advantages of the ball grid array package are:                1) Although the I/O foot-numbers of the ball grid array package increase, the spacing between each foot of the ball grid array package is far larger than the spacing between each foot of the QFP, thereby raising the yield rate of the completed products;        2) The foot-numbers of the ball grid array package per unit area are higher than the foot-numbers of the QFP per unit area. That is, if the foot-numbers of the ball grid array package are the same as those of the QFP, the area of the ball grid array package will be smaller than the area of QFP;        3) Comparing with the QFP, the power dissipation of the ball grid array package is larger. However, the ball grid array package can make use of the welding method of the Controlled-Collapse-Chip Connection, which can be briefly called the C4 welding, to improve the electrical performance of the ball grid array package;        4) Comparing with the QFP, the thickness of the ball grid array package is less shallow than half the thickness of the QFP, and the weight of the ball grid array package can also be reduced to three-fourths of the weight of the QFP;        5) The ball grid array package can apply to a higher frequency band compared to the QFP;        6) The ball grid array package adoptscoplanar welding so that the firmness of on the printed circuit board is better than the firmness of the QFP on the printed circuit board.        
However, the ball grid array package of the prior art also leaves something to be improved. For example, when a printed circuit board is sent for repairs, the repairer can easily dissemble or integrate the QFP on the printed circuit board with his hands or with simple instruments. However, with the ball grid array package on the printed circuit board, the repairing procedure is not that simple. The repairer has to heat the printed circuit board to a certain temperature to melt a plurality of solder balls, which are used for adhering the ball grid array package onto the printed circuit board, in order to dissemble the ball grid array package from the printed circuit board. Regarding the re-integration of the ball grid array package to the printed circuit board, the procedure is a more troublesome matter. The repairer needs to plant a plurality of solder balls one by one on the surface of the ball grid array package. Generally speaking, a skillful repairer needs to take 10 to 15 minutes on average for planting all the solder balls one by one on all the solder ball pads on the surface of the ball grid array package. This planting work by hand not only wastes time, but also cannot assure that each solder ball planted to the ball grid array package will be accurately planted on the corresponding solder ball pad since the repairer's eyes will be tired after staring at the ball grid array package for long time.